Respiratory screening and diagnosis are important in today's health care. Asthma and chronic obstructive pulmonary disease (COPD) constitute major health problems in the US. Mechanical ventilators are used increasingly for life support in patients with serious respiratory illness. Traditional pulmonary function tests (spirometry) are often not adequate to provide the respiratory functional information required by health care professionals. The Airflow Perturbation Device (APD) has undergone significant improvements over several years. APD is simple in concept, employing a rotating wheel in the flow path to change flow by 20-45%, with associated small changes in mouth pressure. From these changes, resistance is calculated. APD is simple in operation, requiring only normal breathing for one minute and is useful in children as well as adults. APD can display resistance changes in real time, and can be modified to measure resistance of ventilated patients and made as portable as a camera. We have used APD it its current implementation to measure average respiratory resistance, as well as separate inspiratory and expiratory values, in nearly 1,500 people. The Phase I clinical data shows that the Standard Deviation (SD) for APD is smaller than IOS on identical measurements. Existing competitive commercial Pulmonary Function Testing (PFT) devices include spirometry, forced oscillation (FO, e.g. IOS), and interrupter (Rint). These either require patients to forcefully exhale (spirometers), or are very expensive and very sensitive to airflow leak (forced oscillation, FO, such as IOS), or require complete interruption of airflow limiting data acquired to only one measurement every 3 breaths (Rint). Three major advantages of APD include a requirement for natural breathing only, relatively less effect from airflow leak than in FO, and it provides an order of magnitude more measurements than Rint. APD can be used by young children, ill adults and in elderly patients. Phase I funding enabled us to considerably advance APD to its current configuration. Pre-Phase I APD weight/cost were 10 pounds/$3,500. APD is now 14.7 ounces/$600, and portable. In Phase II we plan to further reduce its size and cost, improve the flow sensor's accuracy and sensitivity, and add additional capabilities including flow-volume display. To bring APD into commercial production (our long term objective), further refinements are necessary. After that, clinical data must be obtained, and regulatory approval must be sought. The market for the APD is huge, including hospitals, clinics, physician's offices, ambulances, and home care facilities. Because of its size and cost and ease of operation, the APD is an ideal device for home use and for pharmaceutical testing of new drugs. In Phase II we plan to test the device on at least 1,750 individuals at 4 different clinics. Chronic obstructive pulmonary disease (COPD) is fourth leading cause of death in the United States; and respiratory screening for Asthma and COPD, and monitoring of therapeutic interventions are important in US health care. Because of its small size, modest cost, ease of operation and sensitivity to small airway function, the proposed device (APD) can effectively and economically screen for respiratory disease, and monitor interventions in patients with COPD and other respiratory disorders. This will improve diagnosis and recognition of therapeutic benefits as well as lower the cost of the health care. [unreadable] [unreadable] [unreadable]